The present invention generally relates to sheet-form building materials, and more particularly relates to cementitious sheet-form materials having an exposed solid surface that is often intended to satisfy desired aesthetic requirements. The invention is particularly adapted to producing cementitious sheet-form materials having a high recycled materials content, and especially a high content of recycled glass. However, the invention is not limited to the use of recycled materials.
Cementitious sheet-form building materials or panels that provide solid surfaces have a wide variety of applications, such as use for counter-tops, table-tops, shower pans, floors, walls and the like. Such panels are conventionally fabricated with a high cement content using an aggregate, such as rock or crushed marble, and normally have a thickness of at least one inch (2.54 cm) and a maximum thickness limited by weight considerations. A suitable solid surface panel should have certain mechanical, thermal, and chemical properties, as well being capable of meeting certain aesthetic criteria. For example, a sheet material measuring 300 cm×50 cm×3 cm thick should have a compressive strength in excess of 40 KPa and a tensile strength greater than 7.5 KPa. Furthermore, for thermal and chemical stability the material should have a high thermal shock resistance, porosity less than 1%, hydraulic permeability less than 1% and a pH less than 10.0. In addition, it is desirable to have a controllable brightness coefficient.
There is a large and growing market for solid surface sheet-form material that have a high recycled content. Such recycled content can most suitably be provided, at least in large part, in the form of recycled glass. However, the difficulty with substituting glass for sand or aggregate in this application is that glass normally results in the loss or degradation of the mechanical and chemical properties needed for solid surface panels. The present invention overcomes the drawbacks of using glass in this application by providing a new cementitious composition and method for making a solid surface building panel that has a high percentage of glass, but which achieves the mechanical, chemical and thermal properties required of such panels. The composition and method of the invention are particularly suited to providing a solid surface panel having a high content of recycled material, and generally a recycle content of at least 60%.
Cementitious and non-cementitious compositions having a glass or recycled component are known, but none are capable of providing a practical sheet form material having a solid surface with the desirable properties described above. U.S. Pat. No. 4,440,576 to Flannery et al. describes hydraulic cements prepared from oxides, which were melted to form a glass, quenched and subsequently ground to a fine size. This process of melting an assemblage of oxides, cooling the melt and subsequently grinding to a fine particle size is virtually identical to the process by which ordinary Portland cement (OPC) is prepared. While the cementitious composition disclosed in Flannery at al can achieve relatively high strengths, it would be expensive manufacture. Moreover, Flannery et al. does not disclosure to use a aggregate in its composition.
It is also known that recycled glass and fly ash, two products recovered from a waste stream, can be alkali activated, typically with alkali silicate solutions, mixed with additional water to provide the proper rheology, cast into molds and cured at between 40-120° C. for between 2-18 h, to make cements with very high compressive strengths. The resulting strengths of these mortars and concretes range from 63-104 MPa for the fly ash systems (U.S. Pat. No. 5,601,643 Silverstrim, et al.), and as high as 92 MPa for the recycled glass systems for producing artificial stone (U.S. Pat. No. 6,296,699 Jin).
U.S. Pat. No. 6,749,679 to Shi discloses to utilize finely divided glass powder plus fly ash, polymerized with sodium silicate plus a lime source (either CaO, OPC or GGBFS). These cements and mortars have moderately high strengths and good acid resistance due to the high degree of polymerization of the silica anions and the high silica content of the system.
More typically, recycled glass with a surface greater than 300 m2/kg has been used as a traditional pozzolan cement additive, or more recently as an inter-ground additive to cement clinker. With the addition of finely divided glass to act as a cement or cement modifier, there is no penalty, with actual benefits reported in strength gain, lowered hydraulic permeability and greater bond strength.
When recycled glass is incorporated into a cement system as a pozzolan, either as a replacement or addition to the existing cement load, there is an enhancement of properties. In fact high strength mixes can be made using conventional curing cycles by using a moderate amount of glass pozzolan in conjunction with micro silica.
In one study (The Waste and Resources Programme “WRAP”, CONGLASSCRETE II, Final Report, March, 2004), 30% of the OPC was replaced by recycled glass pozzolan with a surface area greater than 300 m2/kg. In the same study recycled glass was added as a pozzolan and as a fine and coarse aggregate replacement for a total recycle glass content ranging between 24-53%. Table I below provides compositions and compressive strengths of these known concrete systems which use recycled glass as a pozzolan as well as an aggregate. The samples are ranked in Table I in descending order beginning with the highest pozzolan/cement ratio and lowest W/Cm ratio. What is noteworthy is the high 28-day strengths obtained with low cement levels. Samples 6 and 7 have high pozzolan to cement ratios, satisfactory 28-day strengths but low recycled content.
TABLE I(WRAP)Reported compositions of pozzolan glass addition to OPC andthe resulting 28-day compressive strengths.SampleCementGP + MS(GP + MS)/fc28Number[%][%]CementW/Cm[Mpa]112.01.300.11.40075.2212.01.300.11.55254.0312.01.300.11.56746.5410.03.300.33.44743.0510.03.300.33.55038.566.656.651.00.55324.276.653.300.50.49349.5GP = glass pozzolan with a surface area >300 m2/kg.MS = micro-silica.W/Cm = mix water to cement ratio.(GP + MS)/Cement = the pozzolan plus filler to cement ratio.The aggregate (fine and coarse), is conventional.
In U.S. Pat. No. 6,645,289 to Sobolev, there is disclosed an inter-ground cement clinker with gypsum, GGBFS, fly ash, pozzolanic glass powder and an admixture comprising a HRWR, a polymer and finely divided silica. In one example, fc28=180 MPa concrete was prepared with 14.5% ordinary Portland cement, 33% pozzolans comprising gypsum, zeolite fines and glass fines, using a W/Cm=0.15. Good strength is achieved with low cement content.
U.S. Pat. No. 5,531,823 to Breton describes a high-strength, low pH, low permeability concrete formed using very low cement content. This is made possible by incorporating high percentages of silica fume and silica flour to give a pozzolan-cement ratio of up to 3. The W/Cm ratio (0.947), is very high for a high-strength mix. The fc28=85 MPa, and the long-term pH is around 9.6. There is uncertainty how the excess mix water is incorporated because the final product is of low permeability. If the water simply evaporates, as the authors suggest, then the final concrete would have a high hydraulic permeability due to the resulting microscopic voids. It is hypothesized that the silica fume is incorporated into the gel phase, reacting with CH to form CHS (Tobermorite). Breton does not disclose a composition that uses glass.
In U.S. Pat. No. 4,505,753 (Scheetz, et al.) high-strength compositions are disclosed with low pH developed by incorporating 40-60% ordinary Portland cement, 5-20% silica fume, and up to 40% finely divided crystalline filler material. The high silica percentage is responsible for the lowered pH. The product requires steam curing.
U.S. Pat. No. 6,080,234 to Clavaud et al. discloses a high performance concretes based on low cement content, by optimizing the uniformity of the particle size distribution from about cm to 5 cm. High strengths of more than 150 Mpa are obtained from mixes with 3-15% of either ordinary Portland cement or high alumina cement, but only after heat-treatments in excess of 200° C.
An unfulfilled need exists for a cementitious composition that has a relatively high glass content, that supports a relatively high content of recycled materials and particularly recycled glass, and that will exhibit the proper set of attributes for a solid surface sheet-form building material, such as excellent mechanical properties, low porosity and hydraulic permeability, pH neutrality and controllable brightness.